Puberty may serve as a window of susceptibility that impacts adult morbidity and mortality, and peripubertal breast tissue may be especially susceptible to environmental exposures. The majority of bone mineral is deposited during teen years, and insulin resistance rises during puberty. Visceral fat is an important factor that increases risk of obesity complications, but little is known about early factors that impact deposition of visceral fat Environmental exposures may impact body composition, as well as pubertal outcomes. Age at menarche is associated with risk of breast cancer, but pubertal growth velocity may be the underlying biologic phenomenon that impacts greater risk of breast cancer in taller women and those with earlier menarche. We will utilize a unique existing cohort of girls followed from ages 6 and 7 and who have had semiannual examinations over 3-5 years. Working closely with the other two BCERC epidemiology projects, and with the Cincinnati BCERC community outreach program, our study proposes to fill the gap towards understanding the relationships between timing of onset and pathway of puberty with menarche, interaction between endocrine disruptors and polymorphisms, and changes in body composition. We will complete the maturation assessment in this established cohort of girls, to include age at menarche, tempo of maturation, age/value of peak height velocity, body composition and fat distribution, and bone mineral accrual during puberty, by pathway into puberty. We plan to assess dimensions of the physical/social environments including exposures to endocrine disrupting toxicants (EDCs), and how these factors contribute to impact onset of puberty and menarche. We will explore the relationships and interactions of EDCs and genetic polymorphisms, on benchmarks of pubertal maturation. The Cincinnati epidemiology and outreach programs will develop and disseminate materials for lay audiences about lifestyle choices and potential health risks of specific exposures in regard to breast cancer, and enhance protocols to report study findings to study families. This proposal should allow us to understand better how changes during puberty can inform future prevention strategies to decrease the prevalence of breast cancer.